A PPT ON DIFFERENT TYPE OF LUNAR ROVERS. AND HOW TO DESIGN IT

1. LUNAR ROVER
Roopkatha Das.
1827047
M-8

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1. Introduction
2. Market Research
2.1 Existing Products
2.2 Technology Research
3.Design for the moon
3.1 Requirements
4. Thank you !

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INTRODUCTION :
Moon exploration is still not considered a thing of the past. Future exploration missions to the moon
will look at creating global maps of unprecedented quality, captured by at least four robotic missions
which will orbit the moon. These exploration missions to the moon, and its mysterious surfaces,
especially those situated around the Polar Regions, will require soft landings in order to map the
surface, examine the volatile deposits and characterise the unusual environment which exists there.
Other plans for moon exploration also include plans to return humans to the moon, however this
time it will not be to prove what man-kind can do, as in the Apollo mission in 1969, but instead it will
ultimately explore how the moon could be used to support a new and growing spacefaring
capability. Whilst on the moon the main aims will be to learn the skills and develop the technologies
which are needed to live and work on another world.
This report outlines the steps taken to design a more advanced moon rover to help with future
exploration missions to the moon. The project has taken inspiration from previous moon rover
designs, however these past designs are still very basic and there are various highlighted instances
where improvements could be made. Such areas for improvements are; designing so that the moon
rover has a more flexible ability to navigate around different terrains, to design to minimise energy
usage to enable a maximum distance to be covered during the mission, and finally to design in the
ability for the moon rover to negotiate terrain surfaces with different terrain surface quality and
hardness.

4. Sojourner Micro Rover:
The Sojourner Micro Rover was one of the first Mars
exploration rovers operating in the late 1990’s for a
duration of 83 earth days. It operated using a non_x0002_rechargeable
battery and a solar panel in order for the
rover to operate through the day. The design is
comprised of 6 wheels, each of diameter 130mm. In this
design each wheel is independently actuated resulting in
high torque to allow for inclines and variances within the
rough terrain. Due to the high torque being incorporated
within the design the Sojourner Micro Rover can only
achieve a top speed of 0.4m/min.

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Spirit Rover:
The Spirit Rover is another NASA designed Mars
Rover. Originally designed for a 90 day mission, the
Spirit Rover operated for more than 6 years due to
environmental events resulting in activity between
the years of 2004-10. In terms of the power
requirements within this design, the rover used solar
arrays and rechargeable batteries which in turn
allowed for 4 hours of activity during one Martian day.
This energy could be stored for use at night. With 6
independently motorised wheels the rover could
achieve a maximum speed of 3m/min and stability on
tilts of up to 30 degrees.

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ATHLETE Rover:
ATHLETE (All-Terrain Hex-legged Extra-Terrestrial Explorer) is a system which is currently under
development for use on lunar rovers. Its 6 legs offer the design the ability for movement with 6
degrees of freedom and the design of these legs allow the rover to both roll and walk over difficult
terrains. With a leg reach in the region of 6 meters this allows the rover to operate on slopes of 35
degrees, this is a larger slope than conventional rocker-bogie drive systems can obtain. (NASA,
2008) In the context of the moon rover design project, this existing design again highlights the
importance of flexible travel and the part this plays in how the rover will be able to negotiate the
different terrains which it may face. As this is an on-going development the team feel that this
design is important as some of the included hardware in this
design is more technically advanced that what has been
expressed previously through the research shown on the other
rover designs from NASA missions. In this case the team feel
that a lot of lessons can be learnt from this development and
therefore refining and further development of these ideas
within the design project could prove to be very beneficial.

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The main technological areas, mainly identified from the previously conducted
research, which were highlighted by the team as areas which would be the key focus
areas for this design project, were the drive system requirements and the use of a
Rocker Bogie suspension system. The team felt that by combining these two elements
the most satisfactory outcome, in terms of flexibility and the ability to move over
differing terrains would be achieved through the use of this type of design.
DRIVE MECHANISM :
• 4, 6 and 8 wheel drive systems are commonly used to help provide stability within the
design, especially where traversing over inclined terrain is a possibility.
• Walking and rolling drive systems have been tested in locations such as Mount Spurr Alaska
or on active volcanoes to prove terrain navigation concept and ability.
• All battery operations (normally lithium battery) are now controlled with recharge systems
such as solar radiation.
• Engineers are in the early development stage of skid steer. This is a drive system where
wheels on either side are synchronised allowing each side of the frame to move
independently. This provides a 0 degrees pirouette capability within the rover design
resulting in good movement control however this often results in the rover tearing up the
surface of the ground on which it is moving. This type of system does not involve the use of
a rigid frame in order to provide better balance capabilities within the rover. This is shown
through the Ratler design example.
• Over the past decade development of the rocker bogie suspension system, which is now
used in Mars exploration, has been rapid. This design is regarded as the best design for
vehicle stability and obstacle climbing capability. (NASA, 2003)

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Rocker bogie suspension :
The main technical aspects of a Rocker Bogie Suspension system are discussed below;
• There are two primary components within a Rocker Bogie suspension system, the
Rocker
and the Bogie. This shown clearly in one of the images below.
• These two elements are connected via a free rotating pivot; this is again
demonstrated in
the image shown below.
• The design has 6 joints that must be reliably locked after deployment. One joint is
motor
driven for deployment.
• Yoke and clevis design for a rocker bridge joint (motorised deploying joint)
withstands 714
N-m bending load and 506 N-m torsional load.
• Latch pawl locks into place on the deployed arm, this changes the state of the micro
switch
used within the design and subsequently sends electrical signals to state that the arm
is
successfully locked and ready for deployment. (NASA, 2003)

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In 2005 Michelin introduced the Tweel. The Tweel consists of a central hub connected to a rigid
outer rim by flexible spokes. The spokes and hub are made of plastic structures that deform when
the tire goes over rough terrain, within the context of this project, the terrain discussed here would
be similar to the differing quality and hardness of terrain of the lunar surface. This enables a large
portion of the tire to stay in contact with the surface, even over uneven terrain, which provides
traction and stability. As previously discussed this is a major requirement of any new developments
within lunar rover design as flexibility and the ability of the lunar rover to move over differing types
of surface are now key design requirements.
The deformable hub and spokes also act as shock absorbers that help reduce the vibrations felt by
the vehicle. Additionally, the tire functions well even if some of the spokes are damaged. At high
speeds the Tweel has run into some problems with noise, vibration, heat, and wear. With designing
for the lunar rover in mind, this would not cause many issues as the intention of the design is to
travel at low speeds with high torque.
In other tire developments, a next generation tire for the Humvee is made of polymers and has
the nterior structure of a honeycomb. The honeycomb structure can support heavy loads and has
lots of room for shrapnel to pass through, while still offering a relatively smooth ride.
Additionally, if as much as 30% of its cells are damaged, the tire suffers little performance loss.
Humvees can currently travel on a flat tire because of their insert design, but testing shows that
the honeycomb design enables them to travel significantly faster and further. This style of design
would obviously also be beneficial to any lunar rover design due to its strong durability and ability
to withstand large amounts of force and pressure.

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In 2009 the Spring Tire was installed on NASA’s
lunar test vehicle, which had a successful ride
through the Johnson Space Centre Planetary
Analogue Test Site, (aka “rock yard”). There are
obvious benefits to using this tire design within
any design produced within the context of this
project. Firstly this tire has been developed for
specific application on the moon, therefore the
functional aspect of this design will have great
focus and detail within the design to produce
the best
result once the rover has reached the lunar
surface. The design in this tire also means that
if any
design changes are required, then extensive
testing of specific expected conditions can take
place
with appropriate mechanical test values being
applied. This will ensure the wheel is fit for
purpose.
In the case of the other designs, testing may
not be specific to use on the lunar surface,
therefore
caution will have to be applied, and resulting in a
longer testing time period before the tire can
be
used within any lunar application.

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Considering the harsh
environment in which the lunar
rover will be used, there are
clearly going to
be issues which may affect the
functionality of the lunar rover
design and the components which
have been used to construct it.
Some of these key issues include;
• Abrasion and wear on parts that
contact regolith
• Vacuum welding of metals,
which may require special coating
and treatments.
• Electrostatic properties of
regolith will cause it to adhere to
and penetrate bearings,
structural connections, viewing
surfaces, solar panels, radiators
and antennas.
• Strategies must be put in place
to create effective vacuum seals
(e.g. for door locks) .

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As the identified environment in which this design has to operate successfully, then designing for
lunar requirements is the most important design aspect within this project. The focus is on choosing
and testing components that may be of concern to a mechanical designer. This includes any
component which may fail under loading during any operational aspect of the lunar rover
functionality, such as deployment or simply navigating the lunar surface. These components can
vary from mechanical components (bearings, fasteners, and lubricants), motors, materials and an overview of
power systems. Component design and selection for use on the moon is driven by the
application and the environment. As has been discussed already, the lunar environment can vary
depending on the region of the lunar surface which the rover may be navigating. This environment
includes moon dust, uneven surfaces, slopes and regions which little information is known about, i.e.
the Polar Regions. For this reason it is important to consider legacy. Legacy “refers to the original
manufacturer’s level of quality and reliability that is built into the parts which have been proven by
(1) time and service, (2) number of units in service, (3) mean time between failure performance, and
(4) number of use cycles.” If a candidate component has a successful legacy, then a designer should
strongly consider using it. As the research presented above has highlighted many instances where
several components have been used successfully within the design of a rover, then these
components will be considered for use in this design due to their proven ability to operate within the
intended environment.

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Thanks!